Method for separation of mixture of polyester and cellulose derivative

ABSTRACT

A method for the separation of a mixture of a polyester and a cellulose derivative comprising introducing gas bubbles into an aqueous liquid medium containing the mixture of the polyester and the cellulose derivative, optionally in the presence of at least one wetting agent and at least one flotation agent thereby separating the mixture by flotation into the polyester and the cellulose derivative.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for the separation of a mixture of apolyester and a cellulose derivative. More particularly, this inventionrelates to a method for the separation of a mixture of a polyester and acellulose derivative into each material by introducing gas bubbles in anaqueous liquid medium containing the mixture of the polyester and thecellulose derivative.

2. Description of the Prior Art

No method for separating a mixture of a polyester and a cellulosederivative is known due to the close similarity in physical properties,such as specific gravity and the like, of these materials. Therefore, amixture of a polyester and a cellulose derivative, for example, filmscraps resulting from the manufacturing of photographic films, has beendisposed of as a waste material.

SUMMARY OF THE INVENTION

An object of this invention is to provide a method for easily andefficiently separating a mixture of a polyester and a cellulosederivative into each of the materials.

The present invention provides a method for separating a polyester froma cellulose derivative which comprises introducing gas bubbles into anaqueous liquid medium containing a mixture of the polyester and thecellulose derivative and thereby floating the polyester. An embodimentincludes a method for separating a cellulose derivative from a polyesterwhich comprises introducing gas bubbles into an aqueous liquid mediumcontaining a mixture of a polyester and a cellulose derivative in thepresence of a wetting agent and a flotation agent and thereby floatingthe cellulose derivative.

DETAILED DESCRIPTION OF THE INVENTION

As a result of extensive studies on methods for the separation of amixture of a polyester and a cellulose derivative, the present inventorsfound that a polyester and a cellulose derivative differ from each otherin wettability by water, i.e., the cellulose derivative is wettable bywater whereas the polyester is hardly wettable by water, and therefore,polyester which is hydrophobic can be floated due to adherence of thebubbles to the polyester thereby floating the polyester. The inventorsalso found that if a wetting agent is present in the water the polyestercan be rendered more hydrophilic than the cellulose derivative wherebythe cellulose derivative can be floated by adhering to bubblesintroduced in the presence of the flotation agent. The method of thisinvention is based on these findings.

The term "polyester" as used throughout the specification and appendedclaims is employed to designate high molecular weight substances havingan ester bond in their main chain and includes materials such aspolyethylene terephthalate, alkyd resins, unsaturated polyester resins,maleic acid resins and the like.

The cellulose derivatives to which the method of this invention isapplicable include cellulose diacetate, cellulose triacetate,nitrocellulose and the like.

The shapes and sizes of the polyester and the cellulose derivativesubjected to the method according to the present invention are notcritical and can vary. It is suitable, however, that the mixture ofthese materials be comminuted into pieces having a size less than about50 mm, preferably 1 to 10 mm either as a film or granules where a largequantity is to be treated.

In a first embodiment of the present invention wherein a cellulosederivative is floated, a mixture of the polyester and the cellulosederivative is mixed with an aqueous liquid medium such as water or saltwater and at least one wetting agent. Suitable examples of wettingagents are alkali metal and alkaline earth metal salts of ligninsulfonic acid such as sodium lignin sulfonate, calcium lignin sulfonate,magnesium lignin sulfonate, etc., an organic colloid and mixturesthereof. The term "organic colloid" used herein refers to hydrophilicorganic colloids which render the surface of the polyester morehydrophilic than the surface of the cellulose derivative therebyincreasing the wetting characteristics of the cellulose derivatives.Such hydrophilic organic colloids are well known in the art in the fieldof ore processing as described in, for example, A. F. Taggart, Handbookof Mineral Dressing Ores and Industrial Minerals, 1948, 12-33 to 12-34,John Wiley and Sons, Inc., New York. Suitable examples of thehydrophilic organic colloid which can be used in the present inventionare tannic acid, a quebracho extract, gelatin, glue, saponin and thelike. These hydrophilic organic colloids can be used alone or as amixture of two or more colloids. The amount of the wetting agentemployed suitably is up to about 1,000 g per ton, preferably 10 to 500 gper ton, of the raw material (i.e., the mixture of the polyester and thecellulose derivative). It is desirable that the mixture of the rawmaterial and the aqueous liquid medium be stirred for several minutesafter the addition of the wetting agent. To the resulting mixture isfurther added at least one flotation agent. Suitable examples areconventionally known flotation agents such as pine oil, kerosene,cresylic acid, eucalyptus, oil, camphor oil, higher alcohols such aspropyl alcohol, amyl alcohol, etc., methyl isobutyl carbinol, pyridine,o-toluidine and the like. A suitable amount of the flotation agent is upto about 1,000 g per ton, preferably 100 to 500 g per ton, of the rawmaterial. Gas bubbles are then introduced into the aqueous liquid mediumthereby floating the cellulose derivative.

In this first embodiment of the present invention, due to the wettingagent the surface of the polyester which is hydrophobic in naturebecomes more hydrophilic than the surface of the cellulose derivative.Gas bubbles are then introduced into the aqueous liquid medium in thepresence of the above-described flotation agent whereby the cellulosederivative can be floated and separated.

In the second embodiment of the present invention wherein a polyester isfloated, the separation of the polyester and the cellulose derivativecan be carried out by introducing gas bubbles into an aqueous liquidmedium containing a mixture of the polyester and the cellulosederivative whereby the hydrophobic polyester is adhered to gas bubblesto float while the hydrophilic cellulose derivative remains in theaqueous liquid medium.

In this second embodiment of the present invention the above describedflotation agent can optionally be employed. The flotation agent can besuitably used in a proportion of less than about 200 g per ton of theraw material thereby promoting the floating separation of the polyester.

The separation tank which can be used in the present invention can beany type of tank such as a tank which is tetragonal type, regular ornon-regular polygonal or circular and the tank can be a trough type, athickner type or a cyclone type tank.

The generation of gas bubbles can be effected using mechanical stirring,bubbling a gas through the medium, release of a gas dissolved underpressure, evacuation to release dissolved gases, electrolysis or acombination of two or more of these methods. The gases which cansuitably be used include air, oxygen, nitrogen, carbon dioxide, inertgases such as argon, etc.

A suitable proportion of the raw material, i.e., the mixture of thepolyester and the cellulose derivative, to be separated and the aqueousliquid medium in the separation tank can range from about 0.1 to about10 parts by weight of the mixed materials per 100 parts by weight of themixture. The temperatue of the aqueous liquid medium is not critical inthe method of this invention, but is preferably in the range of fromabout 0° to about 70° C, most preferably at an environment temperature(about 15° to about 35° C). Temperatures below about 0° C arepractically not preferred since at such low temperatures the efficiencyof separation of the mixture in the flotation tends to decrease. On theother hand, the use of a temperature higher than about 70° C makes themethod of the present invention uneconomical and, in addition, such ahigher temperature is not desirable from the standpoint of the workingenvironment. The aqueous liquid medium is usually employed at roomtemperature but separation by flotation can be promoted by heating theaqueous liquid medium.

The present invention is carried out in an aqueous liquid medium whichincludes water and salt water. Suitable examples of salt water includesea water, brine, bittern-containing water as well as aqueous solutionscontaining halides such as NaCl, MgCl₂ and MgBr₂, etc., sulfates such asMgSO₄, CaSO₄, K₂ SO₄ and Na₂ SO₄, etc. and bicarbonates such asCa(HCO₃)₂ and NaHCO₃, etc. Water generally is employed as the aqueousliquid medium.

Further, the process of inorganic or organic substances, such as thosesubstances contaminating river water, industrial water, etc., in theaqueous liquid medium does not interfere with the present invention.

As previously described, the present invention provides a method forseparating a mixture of a polyester and a cellulose derivative, forexample, arising in the manufacture of photographic films into each ofthe components of the mixture with an excellent efficiency by utilizingthe surface wettability of the mixture of materials and, in case offloating the cellulose derivative, using a wetting agent. The presentinvention makes it possible to convert a waste material which hashitherto been disposed of into a reusable material as a fresh rawmaterial and therefore has a great advantage from the standpoint ofresource utilization.

The present invention will now be illustrated in greater detail by thefollowing examples. In these examples all parts, percentages, ratios andthe like are by weight unless otherwise indicated.

EXAMPLE 1

A mixture of 50 parts of polyester and 50 parts of cellulose triacetateboth obtained from film scraps arising from the manufacture ofphotographic films after removal of the silver halide emulsion coatedthereon was cut into pieces having a size less than 10 mm and 100 g ofthe resulting pieces was placed in a separation tank of a rectangulartype containing 8,000 ml. of water. Tannic acid was added thereto as awetting agent in a proportion of 250 g per ton of the raw materialpieces followed by stirring for 2 minutes. 200 g of pine oil was placedin the tank as a flotation agent. The mixture was separated into a floatand a residue while introducing gas bubbles into the water for a periodof 10 minutes. Cellulose triacetate contents in the resulting float andresidue thus separated were determined by measuring the soluble matterin the float and the residue using methylene chloride containing 10%methanol.

As a result of the above separation, 46 parts of the polyester having apurity of 99.1% was collected as a residue but the float, cellulosetriacetate, was found to contain a small amount of the polyester. 100 gof tannic acid and 100 g of pine oil per ton of the raw material wereadded to the float and cleaning was carried out by introducing gasbubbles into the water for 5 minutes to collect 46.5 parts of cellulosetriacetate having a purity of 97.5% as a final float. The intermediateproduct in which both the cellulose triacetate and the polyester werepresent was found to be 7.5 parts by weight.

Since the final float and residue thus separated had a remarkably highpurity, each could be reused as a raw material for the manufacturing offilms and other products.

In the same manner as described above, mixtures of various combinationsof an alkyd resin, an unsaturated polyester resin, a maleic acid resinand the like with cellulose diacetate, cellulose triacetate,nitrocellulose and the like were separated into each component.

EXAMPLE 2

A mixture of 50 parts of a polyester and 50 parts of cellulosetriacetate both obtained from film scraps arising from the manufacturingof photographic films after the removal of the silver halide emulsioncoated thereon was cut into pieces having a size less than about 6 mm.100 g of the resulting pieces was placed in a rectangular typeseparation tank containing 8000 ml of water followed by introducing gasbubbles into the water for a period of 2 minutes thereby separating themixed material into a float and a residue. The cellulose triacetatecontents in the float and in the residue thus separated were determinedby measuring the soluble matter contained therein using methylenechloride containing 10% methanol.

As a result of the above separation, 47.0 parts of cellulose triacetatehaving a purity of 99.8% was collected as residue but it was found thatthe float, the polyester, contained a small amount of cellulosetriacetate. Gas bubbles were introduced twice into water for 3 minutesto clean the float thereby collecting 48.5 parts of the polyester havinga purity of 100% as a final float. The intermediate product in whichboth the polyester and the cellulose triacetate were present was foundto be 4.5 parts.

Since the final float and the residue thus separated have a high purity,each could be reused as a raw material for the manufacture of films andother products.

In the same manner as described above, mixtures of various combinationsof an alkyd resin, an unsaturated polyester resin, a maleic acid resin,and the like with cellulose diacetate, cellulose triacetate,nitrocellulose and the like were separated into each component.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

What is claimed is:
 1. A method for the separation of a mixture of apolyester and a cellulose derivative selected from the group consistingof cellulose diacetate, cellulose triacetate and nitrocellulosecomprising introducing gas bubbles into a dispersion of a mixture ofsaid polyester and said cellulose derivative, said polyester and saidcellulose derivative being solid pieces having a size of 1 to 50 mm, inan aqueous liquid medium in the presence of at least one wetting agentto render the surfaces of the polyester pieces more hydrophilic than thesurfaces of the cellulose derivative pieces and at least one flotationagent, whereby said cellulose derivative is floated thereby separatingsaid mixture into said polyester and said cellulose derivative.
 2. Themethod as claimed in claim 1, wherein said polyester is polyethyleneterephthalate, an alkyd resin, an unsaturated polyester resin or amaleic acid resin.
 3. The method as claimed in claim 1, wherein saidwetting agent is an alkali metal lignin sulfonate, an alkaline earthmetal lignin sulfonate, an organic colloid, or a mixture thereof.
 4. Themethod as claimed in claim 3, wherein said wetting agent is sodiumlignin sulfonate, calcium lignin sulfonate, tannic acid, a quebrachoextract, gelatin, glue, saponin or a mixture thereof.
 5. The method asclaimed in claim 3, wherein the amount of said wetting agent is up toabout 1,000 g per ton of said mixture.
 6. The method as claimed in claim1, wherein said flotation agent is pine oil, kerosene, cresylic acid,eucalyptus oil, camphor oil, a higher alcohol, methyl isobutyl carbinol,pyridine, o-toluidine, or a mixture thereof.
 7. The method as claimed inclaim 6, wherein the amount of said flotation agent is up to about 1,000g per ton of said mixture.
 8. The method as claimed in claim 1, whereinthe amount of said mixture is about 0.1 to about 10 parts by weight per100 parts by weight of said aqueous liquid medium,
 9. The method asclaimed in claim 1, wherein said aqueous liquid medium is water or saltwater.